Die for die casting and method of manufacturing cast product

ABSTRACT

According to one embodiment, a die includes a stationary die and a movable die. Between the stationary die and the movable die, a product section which includes a main product section, and a protrusion part protruding from the main product section toward a side of the biscuit section, a first runner configured to guide molten metal toward the main product section, and a second runner configured to guide molten metal toward the protrusion part are formed. The second runner is provided at a position deviated from the first runner three-dimensionally, and overpasses the first runner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2008-050568, filed Feb. 29, 2008, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the invention relates to a technique associated withdie casting.

2. Description of the Related Art

A die-casting die of the cold-chamber die casting system comprises abiscuit section for receiving molten metal from an injection apparatusof a casting machine, a product section that is a space in which aproduct is to be cast, a main runner for guiding molten metal from thebiscuit section toward the product section, and a main gate providedbetween the main runner and the product section, for accelerating theflow speed of the molten metal by sharply reducing the thickness.

Here, the solidification time of molten metal of, for example, amagnesium alloy or the like is very short, and hence in a die-castingdie having a small flow cross-sectional area (i.e., a cross-sectionalarea of a space through which molten metal flows), the product sectionis not filled with the molten metal up to every corner thereof, anddeficient filling occurs in some cases. For this reason, some of thedie-casting dies liable to suffer deficient filling are provided with asub-runner and a sub-gate for performing flow-rate support from thelateral side of the product section in addition to the main runner andthe main gate.

In Jpn. Pat. Appln. KOKAI Publication No. 2002-45956, a die structureprovided with a sub-runner branching off from a main runner isdisclosed. The sub-runner extends to the side of the product section,and communicates with the side-edge part of the product section.

In Jpn. Pat. Appln. KOKAI Publication No. 2002-263820, a die for castinga display cover is disclosed This display cover has a support wallformed by injecting a magnesium alloy into a space of a die. Thissupport wall includes a lower edge section and an upper edge sectionlocated on the opposite side of the lower edge section. At a centralpart of the lower edge section, a cutout part cut out to face the upperedge section is provided. The gate of the die is connected to the cutoutpart.

Incidentally, for example, in a cast product such as the display coverdescribed in the Jpn. Pat. Appln. KOKAI Publication No. 2002-263820, aprotrusion section is present at the edge part thereof. A productsection of a die for casting such a cast product includes a main productsection in which a main part of the cast product situated off theprotrusion section is to be cast, and a protrusion part which protrudesfrom the product section, and in which the protrusion section is to becast. Further, the protrusion part is arranged on the biscuit sectionside of the main product section in some cases.

In such a die, when the main gate is connected to the main productsection, the protrusion part is positioned on the upstream side of themolten metal filling port of the main gate with respect to the moltenmetal flow. Molten metal of a magnesium alloy or the like becomes a flowhaving high directivity because of the inertia, and hence the protrusionpart is hardly filled with molten metal. For this reason, there is thepossibility of defective casting such as deficient strength or the likebeing caused at the protrusion part.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIG. 1 is an exemplary exploded perspective view of a die according toone embodiment of the present invention;

FIG. 2 is an exemplary perspective view of a cast product according tothe embodiment of the present invention;

FIG. 3 is an exemplary view schematically showing the structure of aninternal space of the die shown in FIG. 1;

FIG. 4 is an exemplary perspective view showing a region of thestructure of the internal space of the die shown in FIG. 3 encircled bya line F4 in an enlarging manner;

FIG. 5 is an exemplary view showing an example of a structure of aninternal space of a die;

FIG. 6 is an exemplary view showing another example of a structure of aninternal space of a die; and

FIG. 7 is an exemplary view showing a further example of a structure ofan internal space of a die.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings. In general,according to one embodiment of the invention, a die for die castingcomprises: a stationary die; and a movable die to be combined with thestationary die. When the movable die is combined with the stationarydie, a biscuit section, a product section, a first runner, a first gate,a second runner, and a second gate are formed between the stationary dieand the movable die. The biscuit section is a section into which moltenmetal is to be injected. The product section comprises a main productsection, and a protrusion part which protrudes from the main productsection toward a side of the biscuit section. The first runner isconfigured to guide the molten metal injected into the biscuit sectiontoward the main product section. The first gate is provided between thefirst runner and the main product section at a position on a downstreamside of the protrusion part in a stream direction of the molten metal.The second runner is configured to guide the molten metal injected intothe biscuit section toward the protrusion part. The second gate isprovided between the second runner and the protrusion part. The secondrunner is provided at a position deviated from the first runnerthree-dimensionally, and overpasses the first runner.

According to one embodiment of the invention, a method of manufacturinga cast product by die casting according to the present inventioncomprises: preparing a die which comprises a stationary die, and amovable die to be combined with the stationary die, and in which whenthe movable die is combined with the stationary die, a biscuit section,a product section, a first runner, a first gate, a second runner, and asecond gate are formed between the stationary die and the movable die,(i) the biscuit section being a section into which molten metal is to beinjected, (ii) the product section comprising a main product section,and a protrusion part which protrudes from the main product sectiontoward a side of the biscuit section, (iii) the first runner configuredto guide the molten metal injected into the biscuit section toward themain product section, (iv) the first gate being provided between thefirst runner and the main product section at a position on a downstreamside of the protrusion part in a stream direction of the molten metal,(v) the second runner configured to guide the molten metal injected intothe biscuit section toward the protrusion part, (vi) the second gatebeing provided between the second runner and the protrusion part, and(vii) the second runner being provided at a position deviated from thefirst runner three-dimensionally and overpassing the first runner;combining the movable die with the stationary die; and injecting moltenmetal into the biscuit section.

A die 1, and a method of manufacturing a cast product 2 according to oneembodiment of the present invention will be described below withreference to FIGS. 1 to 4. FIG. 1 shows a die 1 according to thisembodiment.

The die 1 is used for die casting of, for example, the cold-chamber diecasting system. For example, a magnesium alloy, aluminum alloy, or zincally is injected into this die 1 as molten metal by pressure.Incidentally, the die according to the present invention is not limitedto the above materials, and can be widely used for die casting in whichvarious materials are used as molten metal.

FIG. 2 shows an example of a cast product 2 which is a product cast byusing the die 1. The cast product 2 is, for example, a componentconstituting a part of a main body housing of an electronic apparatussuch as a portable computer, or a part of a housing of a display unit ofan electronic apparatus. A housing base constituting a bottom part of anapparatus body, a display cover for protecting a back surface of adisplay apparatus, and the like correspond to the more detailed specificexamples. Incidentally, cast products to which the present invention canbe applied are not limited to the above examples, and various otherproducts may be produced.

As shown in FIG. 2, the cast product 2 comprises, for example, arectangular bottom wall 11, and a vertical wall 12 rising from aperipheral edge part of the bottom wall 11, thereby having a box-likeshape opened on one side thereof. The cast product 2 further comprises afirst end part 13, a second end part 14 positioned on the opposite sideof the first end part 13 in the cast product 2, and side edge sections15 and 16 each extending between first and second end parts 13 and 14.The first and second end parts 13 and 14 extend in, for example, thelongitudinal direction of the cast product 2. A cutout part 17 cut outtoward the second end part 14 is provided at a central part of the firstend part 13.

This cutout part 17 is provided to form, for example, a power supplyunit insertion section to which, for example, a battery is detachablyattached, or a display unit foot section to which hinges are attached.Incidentally, the purposes of providing the cutout part 17 are notlimited to the above examples, and a cutout part provided for varioususes corresponds to the cutout part mentioned in the present invention.

As shown in FIG. 2, the cast product 2 comprises the cutout part 17, andthus comprises a pair of protrusion sections 22 a and 22 b protrudingfrom corner parts defined by the first end part 13, and the side edgesections 15 and 16 toward the opposite side of the second end part 14.That is, the cast product 2 comprises a main part 21, and the protrusionsections 22 a and 22 b. The main part 21 is the remaining part of thecast product 2 excluding the protrusion sections 22 a and 22 b.

The protrusion sections 22 a and 22 b are provided separately from eachother at both end parts of, for example, the first end part 13 in thelongitudinal direction. The cutout part 17 is provided relatively largeto occupy a large part of, for example, the first end part 13, and isformed larger than, for example, the total of the protrusion sections 22a and 22 b. An example of the cast product 2 is a thin-walled producthaving a fundamental thickness of, for example, 0.6 mm or less.Incidentally, “fundamental thickness” implies a standard thickness ofthe product, and a thickness which is adopted most widely throughout theproduct. Incidentally, the die according to the present invention mayalso be used for casting exceeding 0.6 mm in the fundamental thickness.

As shown in FIG. 1, the die 1 comprises a stationary die 31, and amovable die 32 to be combined with the stationary die 31. The stationarydie 31 is fixed to a stationary platen not shown. The stationary die 31comprises a stationary die plate 33, a cavity member 34, and an inletmember 35.

The stationary die plate 33 is fixed to the stationary platen, andcomprises a recess part (not shown) on a surface opposed to the movabledie 32. The cavity member 34 is attached to the recess part, and isopposed to the movable die 32. The cavity member 34 comprises a diesurface for forming, for example, an outer surface of the cast product2. The inlet member 35 comprises a through-hole into which an injectionplunger of the casting machine is inserted, and is a cylindrical shape.

On the other hand, the movable die 32 comprises a movable die plate 36,a core member 37, and a dividing piece 38. The movable die 32 is fixedto a movable platen (not shown), and is to be advanced and retreatedbetween a die closed position in which the movable die is combined withthe stationary die 31, and a die opened position in which the movable 32is separated from the stationary die 31.

The movable die plate 36 is fixed to the movable platen, and comprises arecess part 36 a on a surface opposed to the stationary die 31. The coremember 37 is attached to the recess part 36 a, and is opposed to thestationary die 31. The core member 37 comprises a die surface forforming, for example, an inner surface of the cast product 2.

When the movable die 32 is combined with the stationary die 31 as shownin FIG. 3, an internal space 41 into which molten metal is pressed isformed between the stationary die 31 and the movable die 32. FIG. 3 is aview obtained by viewing the internal space 41 as a plane forconvenience of explanation. In FIG. 3, molten metal flows from above tobelow in the figure. Incidentally, in this description, when the term“upstream side” is simply used, it implies the upstream side withrespect to the molten metal mainstream flow, and when the term“downstream side” is simply used, it implies the downstream side withrespect to the molten metal mainstream flow. Here, the molten metalmainstream implies the molten metal flowing through the main gate, to bedescribed later.

As shown in FIG. 3, the internal space 41 in the die 1 comprises abiscuit section 42, a product section 43, a fan gate 44, a first sidegate 45 a, 45 b, a second side gate 46 a, 46 b, an overflow section 47,and a chillvent section 48. To be more specific, the fan gate 44comprises a main runner 51, and a main gate 52. Each of the first sidegate 45 a, 45 b comprises a first sub-runner 53, and a first sub-gate54. Each of the second side gate 46 a, 46 b comprises a secondsub-runner 55, and a second sub-gate 56.

The biscuit section 42 is formed inside the inlet member 35, and is apart which receives the high temperature molten metal from the injectionapparatus of the casting machine at a high speed. That is, the biscuitsection 42 is a section in to which molten metal is to be injected. Theproduct section 43 is an internal space in which the cast product 2 isto be cast, and comprises a dug-down surface corresponding to the shapeof the cast product 2. As shown in FIG. 3, the product section 43comprises first to fourth edge sections 61, 62, 63, and 64 correspondingto the four sides of the cast product 2.

The first edge section 61 is an example of the main edge sectionmentioned in the present invention. The first edge section 61 is locatedthe most upstream in the product section 43, and corresponds to thefirst end part 13 of the cast product 2. The first edge section 61 isconnected to the main gate 52. The second edge section 62 is located themost downstream in the product section 43, and corresponds to the secondend part 14 of the cast product 2. The third and fourth edge sections 63and 64 are each examples of the side edge section mentioned in thepresent invention. The third and fourth edge sections 63 and 64 extendfrom the end part of the first edge section 61 in the stream directionof the molten metal (i.e., the stream direction of the molten metalmainstream), and correspond to the side edge sections 15 and 16 of thecast product 2.

As shown in FIG. 3, the product section 43 comprises a main productsection 66, and a pair of protrusion parts 67 a and 67 b. The mainproduct section 66 is a space in which the main part 21 of the castproduct 2 is to be cast. The protrusion parts 67 a and 67 b protrudefrom the main product section 66 toward the side of the biscuit section42, and are spaces in which the protrusion sections 22 a and 22 b of thecast product 2 are to be cast.

The first edge section 61 of the product section 43 is cut out towardthe second edge section 62. As a result of this, the corner sectionsdefined by the first edge section 61, and the third and fourth edgesections 63 and 64 comprise a pair of protrusion parts 67 a and 67 bprotruding toward the opposite side (i.e., the upstream side) of thesecond edge section 62. As shown in FIG. 3, the protrusion parts 67 aand 67 b are arranged on the biscuit section 42 side (i.e., on theupstream side) of the main product section 66.

The paired protrusion parts 67 a and 67 b are formed separately fromeach other at both end parts of, for example, the first edge section 61.The first edge section 61 comprises a first section 61 a, which is acentral part situated off the protrusion parts 67 a and 67 b, and secondsections 61 b and 61 c in which the protrusion parts 67 a and 67 b areprovided, respectively.

As shown in FIG. 3, the fan gate 44 is a flow path for guiding themainstream of the molten metal to the product section 43. The fan gate44 comprises, as described above, the main runner 51, and the main gate52. The main runner 51 is continuous with the biscuit section 42, and isconfigured to guide the molten metal injected into the biscuit section42 from biscuit section 42 toward the first section 61 a (i.e., the mainproduct section 66) of the first edge section 61 of the product section43. The main runner 51 comprises an upstream section 51 a connected tothe biscuit section 42, and a downstream section 51 b connected to themain gate 52. The downstream section 51 b of the main runner 51 islargely widened as compared with the upstream section 51 a such that themolten metal is to be guided toward substantially the entire part of thefirst section 61 a of the first edge section 61.

As shown in FIG. 3, the main gate 52 is provided between the main runner51 and the first section 61 a of the first edge section 61 of theproduct section 43. The thickness of the main gate 52 is made smallerthan that of the main runner 51. The thickness of the main gate 52 issharply reduced at a position thereof closer to the product section 43,whereby the flow of the molten metal is accelerated toward the productsection 43. The main gate 52 has, for example, a thickness substantiallyequal to the fundamental thickness (for example, 0.6 mm) of the castproduct 2 at the minimum cross-sectional part of the main gate 52. Themain gate 52 is provided on the extension of, for example, the part inwhich the bottom wall 11 of the cast product 2 is to be formed.

The border between the main gate 52 and the first section 61 a of thefirst edge section 61 of the product section 43 becomes a filling port71 of the molten metal mainstream for the product section 43. That is,the main gate 52 communicates with the product section 43 at a positionon the downstream side of the protrusion parts 67 a and 67 b.

As shown in FIG. 3, the first side gate 45 a, 45 b is an auxiliary flowpath for performing flow-rate support for the product section 43. Eachof the first side gates 45 a, 45 b comprises, as described above, thefirst sub-runner 53, and the first sub-gate 54. The first sub-runner 53is an example of the first runner mentioned in the present invention.The first sub-gate 54 is an example of the first gate mentioned in thepresent invention. Incidentally, the first side gate 45 a, 45 b may beprovided only on one side, i.e., on one of the right and left sidesdepending on the shape of the product.

As shown in FIG. 3, the first sub-runners 53 branch off from both sidesof the main runner 51, and pass around the product section 43, andextend on both sides of the product section 43 along the third andfourth edge sections 63 and 64. The first sub-runner 53 is configured toguide the molten metal injected into the biscuit section 42 toward thethird and fourth edge sections 63 and 64 of the main product section 66.

The first sub-gates 54 are provided between the first sub-runners 53 andthe third and fourth edge sections 63 and 64 (i.e., the main productsection 66) of the product section 43, and supply the molten metal tothe main product section 66 from the sides. The thickness of the firstsub-gate 54 is made smaller than that of the first sub-runner 53.

To be more specific, the first sub-gates 54 are connected to, forexample, the third and fourth edge sections 63 and 64 at the end partson the filling end side of the product section 43. The boundary betweeneach of the first sub-gates 54 and each of the third and fourth edgesections 63 and 64 becomes the filling port 72 of the molten metal forthe product section 43. That is, the first sub-gate 54 communicates withthe product section 43 at a position on the downstream side of theprotrusion part 67 a, 67 b in the stream direction of the molten metal.

As shown in FIG. 3, the second side gate 46 a, 46 b is an auxiliary flowpath for performing flow-rate support for the protrusion part 67 a, 67 bof the product section 43. Each of the second side gate 46 a, 46 bcomprises, as described above, the second sub-runner 55, and the secondsub-gate 56. The second sub-runner 55 is an example of the second runnermentioned in the present invention. The second sub-gate 56 is an exampleof the second gate mentioned in the present invention.

The second sub-runners 55 branch off from both sides of the main runner51 at positions on the upstream side of the first sub-runners 53 in thestream direction of the molten metal, and extend toward the protrusionparts 67 a and 67 b of the product section 43. The second sub-runner 55is configured to guide the molten metal injected into the biscuitsection 42 toward the protrusion part 67 a, 67 b of the product section43.

FIG. 4 shows the sub-runner 55 of the one second side gate 45 a indetail. Incidentally, the other second side gate 45 b also hassubstantially the same configuration. As shown in FIG. 4, the secondsub-runner 55 comprises a first section 81, a second section 82, and athird section 83. The first section 81 branches off from the main runner51, and extends in parallel with, for example, the first sub-runner 53.

Here, as shown in FIG. 4, the first sub-runner 53 is provided at aposition deviated from the main gate 52 three-dimensionally.Incidentally, the expression “deviated three-dimensionally” impliesdeviation in the thickness direction of the die 1. The first section 81of the second sub-runner 55 is provided on the same plane as the firstsub-runner 53.

The second section 82 of the second sub-runner 55 is provided on thedownstream side of the first section 81. The second section 82 isprovided at a position deviated from the first section 81three-dimensionally. The second section 82 extends perpendicularly to,for example, the first section 81, and crosses the first sub-runner 53.

This second section 82 is provided at a position deviated from the firstsub-runner 53 three-dimensionally in order to avoid the first sub-runner53, and hence the second section 82 overpasses the first sub-runner 53.To be more specific, the first sub-runner 53 is engraved in, forexample, the core member 37 of the movable die 32. The second sub-runner55 is engraved in, for example, the cavity member 34 of the stationarydie 31. That is, the first and second sub-runners 53 and 55 extend indirections different from each other with the parting line of the die 1as a boundary between the first and second sub-runners 53 and 55. Theparting line is the boundary surface between the stationary die 31 andmovable die 32. The first and second sub-runners 53 and 55 are incontact with each other at the crossing part.

The first section 81 comprises an extension section 81 a extending froma part at which the second section 82 branches off from the firstsection 81. This extension section 81 a functions as a shock absorptionfor absorbing the shock of the molten metal flow. The third section 83extends in a direction perpendicular to, for example, the second section82.

As shown in FIG. 3, the second sub-gate 56 is provided between thesecond sub-runner 55 and the protrusion part 67 a, 67 b of the productsection 43, and directly supplies molten metal to the protrusion part 67a, 67 b. The thickness of the second sub-gate 56 is made smaller thanthat of the second sub-runner 55.

As shown in FIG. 3, the overflow section 47 and the chillvent section 48are provided on the downstream side of the product section 43. Theoverflow section 47 is a section for receiving air inside the productsection 43 pushed out by the molten metal. The overflow section 47 is asection for reducing the filling resistance of the molten metal in theproduct section 43, and pushing out deteriorated molten metal at a flowtip to the outside of the product section 43. The chillvent section 48is a section having a function of preventing the deteriorated moltenmetal from running out of the die 1.

Next, an example of a method of manufacturing the cast product 2 usingthe die 1 will be described below.

First, the die 1 described above is prepared, and the die 1 is set onthe casting machine. Further, a raw material (for example, a magnesiumalloy) is melted to obtain molten metal. Subsequently, the casting cycleis started. First, the movable die 32 is moved to be combined with thestationary die 31, and then the die 1 is clamped. Then, the molten metalis poured into a sleeve coupled to the inlet member 35, the injectionplunger is forced out at a high speed, and the molten metal is injectedinto the biscuit section 42 of the die 1.

When the solidification of the cast product 2 is advanced to a certaindegree, the movable die 32 moves to open the die 1, and the cast product2 is taken out of the die 1 by ejecting pins. As a result of this, onecycle of the die casting is completed. The cast product 2 taken out ofthe die 1 is subjected to removal processing of a surplus part, therebyobtaining a cast product 2 having the desired shape.

Next, the function of the die 1 will be described below.

The molten metal forced into the biscuit section 42 is first filled intothe main runner 51 having a relatively large flow cross-sectional area.Then, the molten metal flows into the first and second sub-runners 53and 54 also having a relatively large flow cross-sectional area. Themolten metal flowing through the main runner 51 is filled into the mainproduct section 66 of the product section 43 through the main gate 52directly connected to the main runner 51. Further, the molten metalflowing through the second sub-runners 55 is filled into the protrusionparts 67 a and 67 b of the product section 43 through the secondsub-gates 56. Further, the molten metal flowing through the firstsub-runners 53 is filled from the third and fourth edge sections 63 and64 of the product section 43 through the first sub-gates 54.

At this time, the second sub-runner 55 overpasses the first sub-runner53, and hence the molten metal flowing through the second sub-runner 55hardly interferes with the molten metal flowing through the firstsub-runner 53. That is, the molten metal flowing through the secondsub-runner 55 is filled into the protrusion parts 67 a and 67 b of theproduct section 43 without causing much pressure loss.

According to the die 1 configured as described above, and the method ofmanufacturing the cast product 2, it is possible to reduce defectivecasting. FIG. 5 shows a die 91 which is not provided with a secondsub-runner 55 and a second sub-gate 56. Here, the flow of molten metalof a magnesium alloy or the like has a high directivity because of theinertia. For this reason, when the die 91 described above is used, theupstream side corner parts 92 (hatched parts in FIG. 5) of the productsection 43 comprising the protrusion parts 67 a and 67 b are notsufficiently filled with molten metal in many cases. That is, there isthe possibility of the upstream side corner parts 92 being brought intoa rough/fine filled state, causing defective casting problems such asdeficient strength.

FIG. 6 shows a die 91 in which a second sub-gate 56 is provided in amiddle part of the sub-runner 53 for performing flow-rate support forthe main product section 66. Even when the die 91 described above isused, the molten metal has high directivity, and hence the molten metalflowing through the first sub-runner 53 passes through the entrance 93of the second sub-gate 56 having a small flow cross-sectional area, andflows toward the distal end of the first sub-runner 53. For this reason,there is the possibility of the filling of the molten metal from thesecond sub-gate 56 into the protrusion part 67 a, 67 b being notsufficient, and the deficient filling being not solved. Further, it isafter the completion of filling of the first sub-runner 53 having arelatively large flow cross-sectional area that the molten metal flowsinto the protrusion parts 67 a and 67 b through the second sub-gate 56,and hence the filling start timing of the filling from the secondsub-gate 56 is delayed compared with the filling start timing of thefilling from the main gate 52. For this reason, air is liable to be leftinside the product section 43, thus there is the possibility of thedefective casting being caused by gas inclusion and the like.

FIG. 7 shows a die 91 provided with a second sub-runner 55 and a secondsub-gate 56. As shown in FIG. 7, the first and second sub-runners 53 and55 are provided on the same plane, and intersect each other on the sameplane. When such a die 91 is used, the molten metal flowing through thefirst sub-runner 53, and the molten metal flowing through the secondsub-runner 55 interfere with each other at the intersection of thesub-runners 53 and 55, thereby causing a pressure loss. Thus, there isthe possibility of the molten metal being not sufficiently supplied tothe protrusion parts 67 a and 67 b from the second sub-gates 56.Further, there is also the possibility of gas inclusion or turbulentflow caused by the interference inducing a casting defect such as amolten metal wrinkle and the like.

On the other hand, as in the die 1 according to this embodiment, whenthe second runner 55 for guiding molten metal to the protrusion part 67a, 67 b is provided separately from the first runner 53 for guidingmolten metal to the main product section 56, and this second runner 55overpasses the first runner 53 three-dimensionally, the molten metalflowing through the second runner 55 hardly interfere with the moltenmetal flowing through the first runner 53, and pressure loss is hardlycaused. Accordingly, it is possible to supply sufficient molten metal tothe protrusion part 67 a, 67 b into which molten metal cannot be easilyfilled, and prevent defective casting from occurring due to deficientfilling. Further, if the molten metal flowing through the second runner55 and the molten metal flowing through the first runner 53 hardlyinterfere with each other, it is possible to prevent defective castingsuch as a molten metal wrinkle and the like incidental to theinterference from occurring.

In the case where the second sub-runner 55 for guiding molten metal tothe protrusion part 67 a, 57 b is provided separately from the firstsub-runner 53 for guiding molten metal to the main product section 66,it is possible to start filling from the second sub-gate 56 withoutwaiting for the filling of the first sub-runner 53. That is, it is evenpossible to make the filling start timing at which filling is startedfrom the second sub-gate 56 earlier than the die 91 shown in FIG. 6, andthus it becomes possible to perform filling in such a manner that air ishardly left inside the product section 43.

In the case where the first and second sub-runners 53 and 55 extend indirections different from each other with the parting line of the die 1as the boundary, it is possible to realize a cubic interchange of thetwo runners with relative ease without providing a relative complicatedshape on the die surface of the die 1.

In the case where the second sub-runner 55 branches off from the mainrunner 51 at a position on the upstream side of the first sub-runner 53,it becomes easier to supply molten metal sufficiently to the firstsub-runner 53 requiring more molten metal than the second sub-runner 55.This contributes to reduction in defective casting.

The die 1 and the casting method of the cast product 2 according to oneembodiment have been described above. However, the present invention isnot limited to the above embodiment. At the implementation stage of thepresent invention, the constituent elements may be modified and embodiedwithin the scope not deviating from the gist of the invention.

Although in the above embodiment two second side gates are provided, oneside gate may be used, depending on the product shape. Incidentally, inthe above embodiment, the first sub-runner is the first runner mentionedin the present invention, and the first sub-gate is the first gatementioned in the present invention. However, instead, the main runnermay be the first runner of the present invention, and the main gate maybe the first gate of the present invention. In this case, the secondrunner overpasses the main runner three-dimensionally.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. A die for die casting comprising: a stationary die; and a movable dieto be combined with the stationary die, wherein when the movable die iscombined with the stationary die, a biscuit section, a product section,a first runner, a first gate, a second runner, and a second gate areformed between the stationary die and the movable die, the biscuitsection being a section into which molten metal is to be injected, theproduct section comprising a main product section, and a protrusion partwhich protrudes from the main product section toward a side of thebiscuit section, the first runner configured to guide the molten metalinjected into the biscuit section toward the main product section, thefirst gate being provided between the first runner and the main productsection at a position on a downstream side of the protrusion part in astream direction of the molten metal, the second runner configured toguide the molten metal injected into the biscuit section toward theprotrusion part, and the second gate being provided between the secondrunner and the protrusion part, and the second runner is provided at aposition deviated from the first runner three-dimensionally, andoverpasses the first runner.
 2. The die according of claim 1, wherein amain runner and a main gate are formed between the stationary die andthe movable die, the main runner configured to guide the molten metalfrom the biscuit section toward the main product section, and the maingate being provided between the main runner and the main productsection, the product section comprises a main edge section connected tothe main gate, and a side edge section extending from an end part of themain edge section in the stream direction of the molten metal, the firstrunner is a first sub-runner branching off from the main runner,extending along the side edge section of the product section, andconfigured to guide the molten metal toward the side edge section, andthe second runner is a second sub-runner branching off from the mainrunner, and configured to guide the molten metal toward the protrusionpart of the product section.
 3. The die according of claim 2, whereinthe first runner and the second runner extend in directions differentfrom each other with a parting line of the die as a boundary.
 4. The dieaccording of claim 3, wherein the second runner branches off from themain runner at a position on an upstream side of the first runner in thestream direction of the molten metal.
 5. A method of manufacturing acast product by die casting, comprising: preparing a die which comprisesa stationary die, and a movable die to be combined with the stationarydie, and in which when the movable die is combined with the stationarydie, a biscuit section, a product section, a first runner, a first gate,a second runner, and a second gate are formed between the stationary dieand the movable die, (i) the biscuit section being a section into whichmolten metal is to be injected, (ii) the product section comprising amain product section, and a protrusion part which protrudes from themain product section toward a side of the biscuit section, (iii) thefirst runner configured to guide the molten metal injected into thebiscuit section toward the main product section, (iv) the first gatebeing provided between the first runner and the main product section ata position on a downstream side of the protrusion part in a streamdirection of the molten metal, (v) the second runner configured to guidethe molten metal injected into the biscuit section toward the protrusionpart, (vi) the second gate being provided between the second runner andthe protrusion part, and (vii) the second runner being provided at aposition deviated from the first runner three-dimensionally andoverpassing the first runner; combining the movable die with thestationary die; and injecting molten metal into the biscuit section.